Intensive research efforts are being made on the metal used in upper electrodes and lower electrodes, and increasing the permittivity in capacitive dielectric films to ensure a sufficient stored electrical charge as capacitors for DRAM become smaller in scale.
Potential choices for capacitive dielectric films include materials possessing high permittivity such as Al2O3, ZrO2, HfO2, Y2O3, La2O3, STO(SrTiO3), Ta2O5, BST((Ba,Sr)TiO3), and PZT((Pb,Zr)TiO3). Potential choices for electrodes include metals such as Ti, Hf, Zr, Al, Ru, Pt, and Ir, and oxides such as SRO(SrRuO3), RuO2; or nitrides such as TiN, HfN, ZrN.
The electrode shape is mainly cylindrical shape with a high aspect ratio. In some cases, the above all films containing barrier metal films such as TiN or TaN must possess excellent step coverage.
Film forming methods are shifting from the conventional sputtering method to CVD methods that provide excellent step coverage, and mostly utilize the reaction between oxygen and an organo-metallic liquid material.